Phase angle indicator



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-dNaIII May 23, 1944. E. L. GlNz-roN PHASE ANGLE INDICATOR Filed Feb.15, 1942 Om ,.:oum En m A m urzw rattle-.i May 23.1944

Edward L. Ginzton, Rockville cena-e, N. Y., :is-

signor to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporationof New York `Application February 13, 1942, Serial No. 430,764 n 9claims. (ci. 17a-245) The present invention relates, generally, to anovel apparatus and method for the measurement of phase angle betweentwo sinusoidal alternating voltages, and the invention has reference,more particularly, to a novel phase angle indicator for accomplishingsuch measurements.

VPrior art methods of phase angle measurement generally fall in twoclassifications; namely, those of the bridge type requiring balancingoperations in order to secure null indications, and those which indicatephase angle directly on .a conventional meter or other indicatingdevice. In general, methods of the first classification require the useof complex bridge circuits or of phase shifting networks andconsequently necessitate the use of considerable skill in operation andinvolve recalibration for each different frequency used. Prior artmethods of the second type which give direct indication of phase angleon a meter usually give a meter indication which is proportional to themagnitude of the sum of, or theA difference betweenthe reference phasevoltage andthe unknown phase voltage, as well` as upon the actual phaseangle between the voltages. Thus the indicating meter can be calibrateddirectly in phase angle only when the inp'ut reference phase voltage andunknown phase voltageare carefully adjusted to be equal. Suchmeasurement devices also rely upon a sine or cosine law relating theoutput meter reading to the actual phase angle diierence, vso that theactual meter calibration follows such a trigonoand are independent ofbias and ,plate Voltage to a large degree.

A further object is to provide such a novel phase angle indicator whichis compact and portoperation.

metric law. Such a calibration, as well known,

affords reasonable accuracy in measurement over a portion of the scaleand very poor accuracy over about a fifth of the scale adjacent, Aforinstance, to the zero deflection point of the meter.

One ,object of the present invention-is to pro'- vide a novel method andapparatus for the' l device or servo mechanism to enable direct andcontinuous observation and/or recrcling of the phase angle between twoalternating electrical potentials, voltages, or other quantities capableof being converted into electrical waves.

Another object lies in the provision of a phase angle indicator whichconsists of components so designed that their characteristics aresubstantially independent of aging of and variation in able and whichisreadily and easily calibratable and which requires no great skill foraccurate Another` object of the present invention is to providel a novelphase angle ,indicator whose reading is' substantially independent ofwide variations in the magnitude of either or both ofthe impressedvoltages.

Still another object of the invention lies in the 4provision of a novelphase angle indicator wherein the instrument calibration is independentof frequency over a very wide frequency range, such, for example, as theentire audio range.

Other objects and advantages will become apparent from thespeciflcation,taken in connection with the accompanying drawing wherein one embodimentof the invention is illustrated.

In the drawing:

Fig. 1 is a wiring diagram of the apparatus of the present invention.

Figs. 2, 3, 4, 5, and 6 are explanatory graphs.

The phase angle indicator of this invention comprises two similarchannels each adapted to receive a respective one of the sine wavesWhose phase'angle difference is to be measured. Each of these channelsconsists of a plurality of ampliers and limiters,y which serve ytoamplify and limit each wave a sufficient number of times so that thesine waves become square waves, the limiters being so adjusted that thesquare waves are of equal amplitude. These square Waves are and limitingone sine wave h s input leads 9 and amplifier I' adapted to receive thesecond sine wave at leads H, H. Amplifier I feeds into limiter 2 whichin turn supplies amplifier 3', the output of which is supplied throughlimiters 4', 5 to the sum-circuit 6', the output of which includes theresistor 30.

vacuum tubes due to manufacturing tolerances 29' produce currents in theresistance 30' inde- The sum tubes 29 and pendently of each other andtherefore, a voltage appears across this resistance which is thealgebraic sum of the square waves. The voltage across resistor 30 isrectified by means of a diode 36 and connected lter circuit and a directcurrent meter 8 may be employed for directly indicating the phase anglebetween the two waves.

'I'he signal supplied to leads 9, 9' is placed across a potentiometerI2, the tap I3 of which may be adjusted to place any desired portion ofthat input voltage across the cathode and first grid of pentodeamplifier tube I4. Tube I4 is shown as an element of a conventionalfeedback type of amplifier circuit, the screen grid of tube I-4 beingattached directly to the cathode, a feed: back resistor I5 beingsupplied -between ground and the cathode of tube I4, the plate voltagefor the tube being supplied by battery I6 through lead 3| and resistorI1 and also to the second grid of tube I4 through resistoxIB. Screenbypass condenser I9 is provided between the screen grid of tube I4 andresistor I8, resistor I8 being large compared to feedback resistor I5and preventing short-circuiting of resistor .I5 through by-passcondenser I9.

The output of the amplifier I is fed through blocking condenser 20intolimiter 2, this output being an amplified alternatingcurrent voltagewith characteristics specially suited for use in the present invention.It is well known in the art that the output of such a feedback ani- Thisoutput voltage is introduced into limiter circuit 2 through resistor 2|and is placed in parallel upon a plate and a cathode of separatesections of double diode limiter tube 22. On the remaining plate andcathode of the opposite sections of diode 22 are placed bias voltagesfrom bias batteries 23 and 24. Each half of the -diode 22 isnon-conducting as long as the voltage on lead 25 has an absolutemagnitude less than the voltagerimpressed on the tube by batteries 23and 24. If the voltage on lead 25 becomes much larger, one-half'of thediode or the other becomes conducting and prevents any furthersubstantial increase of the voltage on leadr 25, due to the low forwardresistance of that half of the diode. The resultant output of tube 22 isthen substantially a square wave, and if amplifier I has been correctlyadjusted, the sides of this square wave are at approximately right anfgies to the time axis, as is illustrated in Fig. 6.

This output; is then impressed on the control grid of tube25l ofamplifier 3. Amplifier 3 may be of the feedback type and may be exactlysimilar to amplifier I except that no input regulating potentiometer I2need be supplied and that resistor 26 may be replaced by a condenser 21.

The output of amplifier 3 is then an amplified square wave which is fedinto amplitude limiterV whose phase is to be compared to the signalplaced on leads 9, 9' is introduced via leads II, I I into amplifier I',limited by limiter 2', amplified again by amplifier 3', and furtherlimited and corrected in shape by limiters 4 and 5' to appear at theoutput of limiter 5 as a substantially perfect square wave with aminimum of phase distortion. Amplifier I' may be exactly similar toamplifier v I, having a potentiometer similar to potentiometer I2 andcontrolled by knob 45. Limiter 2 is similar to limiter 2, amplifier 3 toamplifierY 3, and limiters 4 and 5 to limiters 4 and 5. The square waveoutputs of limiters 5 and 5Y then bear an exactly fixed phase relationto the alternatingcurrent signals impressed on leads 9, 9', and II, II';and, if limiters 4, 5 and 4', 5' are properly adjusted, are ofsubstantially equal amplitude. y I

The squarerwave outputs of limiters 5, 5' are then introduced into sumtube circuits 6, 5' across potentiometers 28, 28'. By means of the tapson potentiometers 28, 28', exactly equal amplitude square wave signalsmay'be placed on the control grids of feedback amplifier pentode tubes29, 29'. The circuits associated with tubes 29, 29 may be exactlysimilar to those of amplifiers 3, 3'. The algebraic sum of the squarewave voltages appearing at the plates of tubes 29, 29 then appearsacross load resistor 32, the plates of tubes 29, 29 being connectedtogether by lead 3U. Sum circuit amplifier tubes 29, 29' act to isolateone channel of the device from the other, so that the component outputvoltage appearing in resistor 32 due to one channel does not influencethe action of the other channel. If the two component square wavevoltages are in phase (the original alternating current voltages havingbeen in phase), the voltage drop across resistor 32 will be of thecharacter shown in Fig. 2. If the component square wave voltages are outof "phase, Fig. 3 repre-` sents the character of the voltage acrossresistor 32 as a function of time; and if the voltages are exactly outof phase, there is seen, as is shown in Fig. 4, to be zero voltageacross the resistor 32. Inspection of Figs. 2, 3, 4 indicates that theduration of current iiow to ground in resistor 32 is proportional to thephase angle be- Y ,tween the two component square wave voltages,

and is thus also proportional to the phase angle between the twooriginal input alternating current voltages impressed on amplifiers I,I'.

Vacuum tube voltmeter circuit 1 may be used l to convert this squarewave current to a direct current which is linear in Vphase differencebetween the two original alternating currents. The sum of the squarewave voltages appearing across resistor 32 is placed through resistor 34on the plate of diode 36 which is connected through resistor 35 to thegrid of one side of twin triode 31, the grid of the other side of'twintriode 31 being tied to the cathode of diode 36, to which the cathodesof tube 31 are also connected through resistor 4I. The plates of twintriode 31 are placed across potentiometer 38, which is suppliedwith anadjustable tap 42 connecting to the positive side of battery I6, thedirect current voltage appearing across potentiometer 38 then beingapplied to the terminals of meter 8, which may be a conventionalmilliammeter, by means of leads 43, 43.

Diode 36 acts to rectify the square wave current fiowing throughresistor 34. The resultant square positive current pulses flowingthrough resistor 35 are averaged by resistor 35 in cooperation withcondenser 44. The twin triode tube 31 acts' as a push-pull. directcurrent -amplier of the direct current voltages placed on its'controlgrids, its cathode bias voltage being supplied by resistor IiI. `Thisconstruction Aclimi-- nates a biased battery which would otherwise benecessary in series with meter B and which would `requirefrequent-adjustment.

The amplified direct; current of this averaging type vacuum tubevoltmeter 1 is then measured directly by meter 8. With the circuitconstants of the amplifiers and limiters correctly designed, theindication of meter 8 may be conveniently made linear with phase angle,as shown by the graph of Fig. 5, over a frequency range of from 250 to10,000 cycles per second, or over a greater range, as desired. The twoinput sine waves whose relative phase angles are to be determined do notneed to be of the same amplitude. Potentiometer I2 in amplifier i andthe corresponding potentiometer in amplifier I' controlled by knob 45may be adjusted so that these input voltages are of the same order ofmagnitude. The instrument Ymay be conveniently designed to operate oninput voltages varying from 0.5 to 5 R. M. S. volts without the use ofadjusting potentiometers I2. The lower limit can be extended by the useof additional amplifying and limiting stages, as previously suggested,between limiters 4, 4' and limiters 5, 5'. In this manner, the devicecan be used to indicate phase angles not only betweensmall or largeinput voltages, but also between voltages which are greatly differentfrom one another.

Standard methods well known to the art may be used to obtain thecalibration curve of meter 8. A'convenient method of calibration is thefollowing three point scheme. A voltage of any available frequency isapplied to the input leads of amplifier I, the input leads of amplifierI' being short circuited. The volume control potentiometer 28 in sumcircuit 6 is adjusted to produce a half scale deflection (90) of meterB. Then, similarly, the same voltage and frequency is introduced intoamplifier I', the input leads .to amplier l being short circuited, andthe volume ,control potentiometer 28' in sum circuit t' is adjusted toproduce half scale deflection on meter 8. Then the samel voltage isapplied simultaneously to the inputs of both amplifiers I, I', producingfull scale deection of meter 8. Then the voltage on one of the ampliersis reversed in phase, as by means of a transformer known to have zerophase shift, and the meter Ii has zero deflection, corresponding to the180 point on the scale. As the calibration is linear, further points canbe obtained in thi.i well known manner.

It is seen that modifications of amplifiers I, i', 3, 3', limiters 2,2', 4, 4', 5, 5', and vacuum tube voltmeter 'I may be made at willwithout departing from the scope of the present invention. Also, as manychanges could be made In the above construction and as many apparentlywidely different embodiments of this invention could be made withoutdeparting from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingshould be interpreted asl illustrative and not in the limiting sense.

What is claimed is:

1. A phase angle indicator comprising a plurality of independentchannels, each channel being adapted to receive a respective one of thetifying andlterin'g the current flowing through said impedancepand meansconnected to said rectifying and filtering means for measuring theresultant averaged current to thereby provide an indication of the phaseangle between said waves.

2. A phase angle indicator as dened in claim 1 wherein said meteringmeans comprises a push-V pull amplifier supplied with said averagedcurrent andv a direct current meter connected across theY output of saidamplifier.

3. A method of. measuring the phase angle between two sinusoidal wavescomprising the steps of separately amplifying and limiting saidrespective waves to produce substantially square waves, adjusting saidsquare waves to waves of Vequal amplitude, taking the algebraic sum ofsaid waves, rectifying and filtering the resultant of said waves, andthereafter metering the average current so produced.

4. Apparatus for measuring the phase angle between two alternating wavescomprising amplifiers for separately amplifying each of :said waves,limiter means for limiting said amplied waves to produce substantiallysquare waves, in-

I tegrating circuits connected to said limitersfor equalizing theamplitude of said substantially square waves and for producing thealgebraic sum of said substantially square waves, and metering means fedby said algebraic sum and serving to indicate directly the phase anglebetween said alternatingfwaves.

5. Apparatus for indicating the phase angle between two alternatingwaves comprising amplifier and limiter means providing se'parate inputchannels for changing said waves to substantially square shape, variablemeans lfor adjusting the output of at'liast one of said amplifier andlimiter means for obtaining exactly equal amplitudes in saidsubstantially square waves, means for superposing and combining saidsubstantially square waves, and means for converting the algebraic sumof said substantially square .waves into sensible indications of phasedisplacement between said waves.

6. In the apparatus defined in claim 5, said means for superposing andcombining' the lwaves comprising a load common to the output of bothchannels, and means for measuring the average current ow through saidload. Y

'7. Apparatus for measuring the phase angle between two alternatingwaves comprising amplier and limiter means providing separate inputchannels for saidrwaves and producing output waves of substantiallysquare form, a common load directly coupled to the output waves of bothchannels, and means connected to said load for converting the algebraicsum of 'said waves into sensible indications of the phase displacementbetween said waves.

8. Apparatus for measuring the phase angle between two alternatingwavescomprising separate input channels for the respective waves embodyingamplifying and limiting means for changing the waves into substantiallysquare shape, a common load connected across the out;

puts of said channels, means for rectifying the current fiow throughsaid load, means for amplifying the direct current output of saidrectifying means and a meter actuated by said ampli fied direct current.l c

9. Apparatus for measuring the phase angle between twov alternatingWaves comprising separate input channels for the respective Wavesembodying amplifying and limiting means for changing the waves intosubstantially square form. at least one of said channels comprisingmeans adjustable for equalizing the amplitude of said substantiallysquare Waves output by said channels, means connecting the outputs ofsaid amplifying and limiting means to a common load, and meansresponsive to the resultant current ow through the load for sensiblyindicating directly the phase angle between said waves.

EDWARD L. GINZTON.

